A Complete Approach to Flowsheet Development

International Laterite Nickel Symposium - 2004 k e s s Develo~mEdited by W.P. Imrie. D.M. Lane. S.C.C. Baniett. R.M. Berezowsb, E.J.M. Jahnsen. P.G. Mason. J.A. Murray, R.C. Osborne. J.G. Reid. J.G. Schofield. L.E. Seeley, I.G. Skipper and Y.M. Torres TMS (The Minerals, Metals & Materials Sociew), 2004

A COMPLETE APPROACH TO FLOWSHEET DEVELOPMENT NIQUEL DO VERMELHO (CVRD) CASE STUDY Mike

dams'; Dwight van der ~ e u l e n ' John ; ~n~ove'

'SGS Lakefield Oretest, 43 1 Victoria Rd, Malaga, Western Australia 6090 Australia Keywords: Flowsheet, CVRD, Nickel, Piloting, Pressure, Leach, Refining. Abstract

A comprehensive pre-feasibility study has been conducted by Companhia Vale do Rio Doce (CVRD) for Niquel do Vermelho nickel laterite deposit. Within this study, five integrated flowsheet options were evaluated via batch and pilot campaigns at Lakefield Oretest, over an intensive six-month period from receipt of ore to final reporting. Key technical objectives set by the client included demonstrating the technical viability of the beneficiation of several ore types, processing through integrated pressure acid leachlmixed hydroxide precipitation (PALIMI-IP) and mixed sulfide precipitation (PALIMSP) circuits, and the treatment of barren liquors to meet stringent environmental requirements. Refining of the MHP was by ammonia re-leach and solvent extraction (SX) to produce LME-grade nickel cathodes, NiCO,, NiO and CoS. LME grade nickel and cobalt was also produced by oxidation of the MSP and hydrogen reduction on the leachate. The database and data acquisition system, along with web-based reporting, enabled rapid turnaround on both daily and more comprehensive run reports, making it possible for speedy and confident decisions on operating conditions of the complex flowsheets. The high value of developing such data is emphasized and discussed as pivotal in the successful progression of laterite projects through to sustainable commercial viability. Introduction

Development of metallurgical flowsheets for the recovery of metal values from ores has often been a lengthy process. Moreover, if the testwork program has been inadequately planned, there is a risk that inappropriate strategic decisions may be made to meet tight schedule deadlines. SGS Lakefield Oretest has developed a sound basis to assist resource companies during their flowsheet development. Integration of process flowsheet definition, batch and pilot testwork with state-of-the-art facilities and modem data acquisition and reporting systems, ensures the rapid delivery of tested process flowsheet appropriate for the ore. This paper presents a case study covering a testwork program designed for such an approach. Lakefield Oretest was commissioned by CVRD to conduct a comprehensive piloting campaign to study the different hydrometallurgical routes associated with processing Niquel do Vermelho nickel laterite ore through beneficiation, pressure acid leaching, and subsequent production of a mixed hydroxide intermediate product (MI-IP), and a mixed sulphide intermediate product (MSP). Both intermediate products were further processed through different downstream refining routes to produce nickel cathode, cobalt sulphide, nickel carbonate, nickel oxide, as well as nickel and cobalt powders, all as finished products. Five flowsheets were devised by CVRD, covering both key routes (MHP and MSP). The prime objective of the program was to demonstrate the technical viability of the PALNHP and 161

PALlMSP process routes on Niquel do Vermelho laterite ores, for producing a range of final and intermediate products. The program covered a six-month schedule, from receipt of the ore to issue of the final report. This included flowsheet definition, batch testwork for definition of process conditions, pilot testwork and comprehensive ongoing reporting throughout the campaign. The schedule is summarized in Table I. Table I. CVRD Program Schedule Duration or Tonnage

Item Batch testwork Beneficiation Runs PALlMHP Run 1 PALlMHP Run 2 PALlMSP Run SXIEW Run Final Report

Date Nov 2002 -May 2003 Nov 2002 Dec 2002 Jan 2003 Mar 2003 Mar 2003 May 2003

4 x lot 7 days 7 days 7 days 7 days

Process Flowsheet Definition

The testwork program to be evaluated in the pre-feasibility study was initially prepared by CVRD, and was designed to cover proven industrial-scale options for processing of nickel laterites through acid leaching. Atter the contract was awarded and prior to commencement of the campaign, a series of discussions was held with the client. A detailed proposal covering all aspects of the program, discussed below in more detail, was developed with the client's requirements and Oretest experience. A schematic process flowsheet diagram for the campaign is given in Figure 1 .

Beneficlation

R1 R2 R3 R4

Blend ore1 Ore 2 Ore 3

R l PAUMHP R2 P A U M H P l

*m productlon

Steam strip

NH strip

Acid strip

)-

Batch H- redn

NiCO ppbr

calcination

Figure I. Schematic process flowsheet diagram for the campaign Drill core samples were received and blended into four representative ore types comprising three different silica grades and a blend. Batch testwork to define the conditions preceded pilot

beneficiation testwork to determine beneficiation response and produce thickened products with grade and size suitable for feed to the autoclave. Batch hydrometallurgical testwork was conducted on representative sub-samples of the various feeds to define conditions for PALMHP Run I in the pilot plant. This was a run to confirm the operating conditions, to fill the circuit and to produce sufficient PAL discharge for batch testwork on the downstream unit operations. This testwork was completed while ensuring sufficient time to implement changes and improvements in process design and determine conditions from the batch work on actual PAL discharge sample for the integrated PALMHP Run 2, and PALIMSP Run 3. [ntermediate MI-IP and MSP products were further processed by continuous and batch testing, to produce the range of final products. Batch Testwork - Process Development

Batch Beneficiation A series of scrubbing and attritioning tests were carried out to define the process flowsheet and required piloting conditions. Several samples were wet screened and shipped to CVRD for successful comparison of methodologies, enabling correlations with earlier batch testwork conducted at CVRD. Spiral testwork successfully produced a chromite concentrate while the use of a Kelsey jig for this duty proved less effective. Settling. Rheologv and Flocculant Screening Settling and rheology tests were conducted on autoclave feed samples and revealed no significant slurry handling issues. A selection of flocculants were successfully compared using 2 m column settling tests to assist in the choice and dosage of an appropriate reagent. Batch Pressure Acid Leach ~ e v e i a batch l PAL tests were conducted using a 4.5 L autoclave, to define the leach conditions for piloting, which specifically included acid addition levels and expected retention times. MHP Process Route Definition Batch testwork was conducted on the major downstream unit operations for the MI-IP circuit to hclp define process flowsheet and conditions for piloting. This work included primary neutralisation, iron removal, MI-IP, ammonia re-leach, partial steam strip, SX, NiC03 precipitation and calcination, and excess barren liquor neutralisation. MSP Process Route Definition and Seed Production Batch testwork was conducted on the major downstream unit operations for the MSP circuit to help define process flowsheet and conditions for piloting. This work included pre-reduction, neutralisation, MSP, pressure oxidation (POX), impurity removal, SX (Cyanex 272), hydrogen reduction, and excess barren liquor neutralisation. A CVRD mixed sulphide precipitation seed to initiate MSP production in the MSP pilot-plant, was initiated using a 20L batch autoclave.

Pilot Testwork Beneficiation Piloting Three runs with -10 tonnes of each of HighIMidlLow Silica samples were conducted after a preliminary run on a blend of all three ore types. Overall mass accountability was 100.0 k 1.5%. The Niquel do Vermelho samples represent a deposit with good nickel grades and impurity levels. Rejection of silica and significant nickel upgrading using conventional scrubbing, size separation and attritioning were demonstrated. A series of conceptual mass balances for a fullscale plant were carried out at several product particle sizes. Results are reported elsewhere [I]. A schematic process flowsheet diagram for the beneficiation pilot plant is given in Figure 2.

Recycle process water

Scrubbing

4

1

I

I .'-Screening

Scrubbing

+6 rnrn +0.5 rnrn rejects rejects

product

rejects

Figure 2. Process flowsheet diagram for beneficiation Hvdrometalluraical Piloting to MHP and MSP Intermediate Products Three separate continuous pressure acid leach runs, each demonstrating the amenability of blended, beneficiated Niquel do Vermelho ores to pressure sulphuric acid leaching (PAL), were successfully piloted. Pressure acid leaching of nickel laterite ores is well establishcd at the commercial scale, minimising project risks associated with this established technology. Excellent extractions for both Ni and Co were consistently achieved. The consumption of acid was relatively low as compared to the broad range of other nickel laterite operations. A schematic process flowsheet diagram for the hydrometallurgical piloting to MHP and MSP intermediates is given in Figure 3. Two piloting runs to produce a mixed hydroxide intermediate product were successfully completed. Re-leaching of the residue from the iron removal stage and secondary hydroxide precipitation circuits, in the second of these runs, was also demonstrated. The two piloting runs produced a combined mixed hydroxide intermediate precipitate product of good quality.

(a) MHP Route rra ld

Resldw R.*.ch

Pmmmum Crld U.rh

mmy N.uhall.atlon

I1 o-.o.

--. YHP I-*

---

"-

v

-

0I.O.w-

J

+Fin. P

o

~

Idllm.

~

7-m.

(b) MSPRoutr IW(S

CCD

A S ~ C C WPnWa.

"W

St-

1" p. mb

PAUPWN

!7ryCf

U n m

E-.

U'

Removal

mmn

u w

S-d

0,-

O

Pllrmlb

t

7

0,-

*

Runoval

~m~unt-.n

RVd.

v -RnbPr&cl

Tallln~.

lo r d m

l o Id-

I

Figure 3. Process flowsheets for hydrometallurgical piloting to (a) MHP and (b) MSP intermediates. Excess barren liquor bled from the manganese removal circuit as CCD wash water was treated successfully to produce a relatively pure effluent for potential disposal to the environment. Impurities in the treated barren liquor from the MHP circuit bleed were well below the maximum allowable levels provided by CVRD for liquid emuent discharge. A mixed sulphide precipitation run, decoupled from the pressure acid leach (PAL) run after the neutralisation stage for safety reasons, was also successfully piloted. Subsequent processing of

the reduced and neutralised pregnant liquor solutions occurred in a mixed-sulphide precipitation plant using hydrogen sulphide gas. This run successfully demonstrated continuous autoclave precipitation of mixed sulphides with Ni recoveries greater than 99 %and with total rejection of Mn and Mg impurities. A good quality mixed sulphide intermediate product was produced. Excess barren liquor bled from the mixed sulphide barren liquor circuit, was further neutralised to remove iron and produce a relatively pure effluent for potential disposal to the environment. The treated barren liquor from the MSP circuit contained impurities well below the maximum allowable levels provided by CVRD for liquid eMuent discharge. Ammonia Re-leach and Partial Steam S t r i ~Piloting A series of bulk batch ammonia re-leach runs was completed, leaching mixed hydroxide product from the two MHP piloting runs. The leachate produced was of good quality. Solvent Extraction and Electrowinninrr (SXEW) Piloting Two separate solvent extraction continuous piloting runs were completed, demonstrating the technical viability of recovering nickel from the partial steam strip liquor using LIX 841. One run used an acid strip, the product from which was stored for a separate electrowinning trial. Several LME-grade cathodes (assaying > 99.99 % Ni) one-tenth of full-scale were produced. The second run used an ammonium carbonate strip, the product o f which was stored for the separate production of a nickel carbonate precipitate. The nickel carbonate was subsequently calcined to produce nickel oxide assaying > 99.5 % NiO.

Batch Testwork - Product Treatment MHP Product Treatment The SX pilot-scale testwork on the MHP product produced a pure, high concentration NiS04 electrolyte for EW and nickel ammonium carbonate pregnant liquor. The latter was treated in further testwork to produce NiO. MSP Product Treatment The pilot-scale MSP testwork produced an intermediate mixed sulfide precipitate product, which was treated in further testwork as follows: POX leaching to dissolve the MSP. Impurity removal of Fe, Cu and Zn by precipitation, cementation and SX. SX batch testwork to produce separate NiS04 and C0S04 pregnant liquors. H2 reduction of NiS04 to Ni metal powder. H2 reduction of CoS04 to Co metal powder.

Reporting Data capture, collation, interpretation and reporting is a crucial activity for an integrated pilot plant campaign of this size. SGS Lakefield Oretest places great emphasis on this aspect of piloting, with a data metallurgist team appointed for this area of the program in addition to the plant operating teams. This approach enables the operating metallurgists to focus on

metallurgical issues based on sound mass balance and concentration and operating profile data. Likewise, the data metallurgy team can focus on resolving any sample preparation, assaying and mass-balancing issues without also having to be concerned about operating the plant.

During the piloting campaign, and specifically during the plant operating periods, the data metallurgists processed all data via databases and spreadsheets so as to build up information progressively towards the final report. This allowed daily metallurgical and control reports to be presented in a timely manner based on control assay information representing live plant conditions with only a few hours lag for sample preparation, assay and data processing. The data included metallurgical recoveries, operating temperatures, pressures, flows and solution chemistry, as well as any operating, safety and environmental issues. This provided good quality key process measurements from which informed decisions were made in time to have a visible impact on plant performance before the run had finished. All data was presented in various forms, ranging from Distributive Control System (DCS), logsheets, raw assays, daily metallurgical and control reports through to trending, campaign summaries and overall elemental balances and accountabilities: 8

8

Daily Reporting covering the previous 24 hours of operations, trends and metallurgy. Weekly Reporting of project management issues. Comprehensive Run Data Pack within I0 days of run completion. Final Report, comprising I l volumes.

This approach ensured speedy and confident set point decisions on the various unit operations in the pilot-plant flowsheets. The quality of the data is enhanced as it is less prone to error by having a dedicated data team processing it. The final campaign report was completed about six months from receipt of ore, ensuring a sound basis for the engineering study. Data Acquisition Systems The pilot-plant database was set up at Lakefield Oretest to ensure effective acquisition and control of data. The diagram in Figure 4 outlines the components of the system. The central component is the Structured Query Language (SQL) Server database, and both Microsoft (MS) Access and Microsoft (MS) Excel were used to extract or input data from the central database. The ability to query the database and instantly plot trends presented the operating metallurgists with a powerful tool to ensure fine control on the various processes. Client Access Website Provision of a secure Client Access Website enabled the rapid communication of key data, photographs, daily and weekly reports in an easily downloadable form to virtually anywhere in the world. This meant that client personnel and consultants could at all times take part in the decision-making process, regardless of other commitments or location.

HiPAL Database Data Components

Figure 4. Data Acquisition System Components

Campaign Outcomes Technical Outcomes Following upfront process flowsheet definition covering the five process options, technical success was achieved on all process routes piloted. High nickel and cobalt leach recoveries were achieved, as well as plant and process availabilities in excess of 99 %. Overall accountabilities for PALIMHP Run 2, as an example, were 101.9 YOfor Ni and 99.0 % for Co. Autoclave plant stability over a representative seven-day run is illustrated in Figure 5. Plant stability achieved can be also seen as a clear indication of the amenability of the ore to HPAL processing. Relatively low pulp viscosity and minimum scale formation or solids accretion resulted in no process related blockages or instability. Management Outcomes The operation integrated both occupational health and safety and environmental management systems, with excellent records for the period. During the course of the 6-month program some 200,000 assays were carried out on about 15,000 samples, the majority of which were sampled, assayed and reported within the four seven-day piloting runs. Comprehensive run data pack reports were released within 10 days of mn completion, including mass balance, profiles, trends, interpretive comments and recommendations. A final report of around 5,000 pages was released within 30 days of the final operation. Program Outcomes High plant availabilities meant that more information was generated during the testwork program for CVRD. Tight schedules were met for the entire campaign, including batch, pilot and reporting aspects. This made for rapid daily and run reporting for effective decisionmaking.

Figure 5. Autoclave control data for a representative 7-day run. Conclusions

The technical, management and program successes of the campaign ensured the rapid availability of meaninghl data and other information for use in the pre-feasibility study. This case study has illustrated the benefits of a complete approach to comprehensive flowsheet development, envisaged by CVRD since the early stages of the Niquel do Vermelho project. Lakefield Oretest was able to provide all piloting and bench scale tests required for testing with high quality procedures, data analysis and results presentation. These benefits are significant, and provide a sound basis for decision making during the course of developing a resource project. Acknowledgements

This paper is published with the permission of CVRD. The success of the campaign was due in no short measure to the excellent technical and operational expertise of the 71 team members, as well as 6 clicnt personnel, every one of whom played an invaluable role in achieving the outcomes of the program. In addition, 13 vendors and consultants were involved to augment various aspects of the program. References

Vanessa M. Torres. 'Wiquel do Vermelho Project - Metallurgical Update," ALTA 2003 I. Nickel/Cobalt-9 Technical Proceedings (Castlemaine, VIC, ALTA Metallurgical Services, 2003), 12 pp.